DFT: Support dft_length and negative axis

[justinchuby]

I was trying to run the BirdNET model: https://huggingface.co/justinchuby/BirdNET, but it was unsupported due to the DFT node.

[kali]

Did some work on for dft "recent" extensions in #1905 . But this model present other challenges, it does not load yet. To be continued.